1. Field of the Invention
The present invention relates to a mobile communication system, in particular, to a received power calculating method of a receiver of a radio portion of a mobile communication system, the receiver calculating a received power and controlling a down-link transmission power of a base station.
2. Description of the Related Art
In the CDMA (Code Division Multiple Access) system, when a base station spreads a spectrum of a transmission signal with a plurality of predetermined codes and communicates with mobile stations using the spread signal, the same frequency band can be assigned to a plurality of subscribers or channels. Thus, frequencies can be effectively used. In the CDMA system, when a receiver receives a spread spectrum signal from the base station, unless the receiver de-spreads the spread spectrum signal with the same code at the same timing, the receiver cannot extract the original transmission signal. Thus, the bit error rate of the received signal deteriorates.
In the CDMA system, a high power transmission signal transmitted from a transmitter disposed in a near location interferes with a weak transmission signal transmitted from a transmitter disposed in a far location. Such a problem is referred to as location problem.
To alleviate such a problem, it is necessary to accurately and widely control a transmission power.
Generally, a transmission power control signal can be generated with the average received power. When a mobile station controls the transmission power of a base station, if the received power calculated by the mobile station is lower than a predetermined threshold value defined in the system, the received power becomes information that causes the transmission power to increase. The information is transmitted from the mobile station to the base station. Thus, the information causes the base station to increase the transmission power by, for example,  dB.
On the other hand, when the received power calculated by the mobile station is higher than the predetermined threshold value defined in the system, the received power becomes information that causes the base station to decrease the transmission power. The information is transmitted from the mobile station to the base station. Thus, the information causes the base station to decrease the transmission power by  dB.
After the transmission power is controlled, the average received power converges on the threshold value in a predetermined time period.
A receiver of a conventional mobile station has a gain changing means and a variable gain amplifying means. The gain changing means and the variable gain amplifying means are disposed upstream of a frequency converting means that converts a radio frequency signal into an intermediate frequency signal. The gain changing means selects a radio frequency amplifying means or an attenuating means so as to prevent the frequency converting means from operating in the saturation region. The variable gain amplifying means controls the gain so that an input power to an analog-digital converting means (A/D converting means) that converts an analog signal of the received signal into a digital signal becomes constant. When the received power at an antenna is relatively high, the gain of the gain changing means is changed so as to prevent the frequency converting means from operate in the saturation region. When the gain of the gain changing means is changed, a control amount corresponding to a gain variation amount of the gain changing means is placed in a gain control signal of the variable gain amplifying means so as to keep the input power of the A/D converting means constant.
To control the transmission power of the base station, the received power is converted into a digital signal by the A/D converting means. The average received power in a predetermined time period is calculated. Corresponding to the calculated result, the transmission power of the base station is controlled.
FIG. 1 is a block diagram showing the structure of a conventional mobile station. Referring to FIG. 1, the mobile station has an antenna 101, an duplexer means 102, a first radio frequency amplifying means 103, a first band pass filter means 104, a gain changing means 105, a second band pass filter means 108, a first local signal oscillating means 110, a frequency converting means 109, a channel filter means 111, a variable gain means 112, a second local signal oscillating means 113, an quadrature demodulating means 114, low pass filter means 115 and 116, analog/digital (A/D) converting means 117 and 118, a digital signal processing means 120, a radio portion controlling means 119xe2x80x2, a transmitting means 122, and a controlling means 121xe2x80x2. The duplexer means 102 separates a transmission signal from a received signal. The gain changing means 105 has an attenuating means 106 and a second radio frequency amplifying means 107. The frequency converting means 109 converts a radio frequency signal into an intermediate frequency signal with a first local oscillation signal of the first local signal oscillating means 110. The channel filter means 111 separates a desired channel from the received signal. The quadrature demodulating means 114 converts the intermediate frequency signal into a base band signal with a second local oscillation signal oscillated by the second local signal oscillating means 113 and a signal phase-shifted by a 90xc2x0 phase shifter, quadrature demodulates the base band signal, and outputs an I channel signal and a Q channel signal. The low pass filter means 115 and 116 pass only base band signals that have been quadrature demodulated.
The digital signal processing means 120 receives the I channel signal and the Q channel signal, performs a de-spreading process, an error-correcting process, and so forth for the I channel signal and the Q channel signal, and supplies the de-spread signals to the radio portion controlling means 119xe2x80x2. The radio portion controlling means 119xe2x80x2 receives the I channel signal and the Q channel signal, outputs signals that control the gain changing means 105 and the variable gain means 112, and outputs a transmission signal.
FIG. 2 is a block diagram showing the structure of the radio portion controlling means 119xe2x80x2. Referring to FIG. 2, the radio portion controlling means 119xe2x80x2 has a received power calculating means 401, a gain changing means controlling means 402, a transmission power controlling means 403, and a transmission signal generating means 404. The received power calculating means 401 calculates the average power of the I and Q channel signals received from the A/D converting means 117 and 118 in a predetermined time period, controls the variable gain means 112 so that the powers of the signals supplied to the A/D converting means 117 and 118 become constant. Further, the received power calculating means 401 supplies the calculated results to the transmission power controlling means 403, the gain changing means controlling means 402, and the controlling means 121. The gain changing means controlling means 402 compares a threshold value of the received power at the antenna means 102 with the average power calculated from the received power calculating means 401 and generates a gain selection control signal of the gain changing means 105 so as to prevent the frequency converting means 109 from operating in the saturation region. The transmission power controlling means 403 calculates the power of the received channel with the average received power value received from the received power calculating means 401 and the de-spread received signal received from the digital signal processing means 120. When the power of the received channel is lower than a predetermined threshold value, the transmission power controlling means 403 generates a control signal that causes the base station to increase the transmission power. In contrast, when the power of the received channel is higher than the predetermined threshold value, the transmission power controlling means 403 generates a control signal that causes the base station to decrease the transmission power. The transmission signal generating means 404 places the transmission power control signal on the transmission signal received from the controlling means 121 and generates transmission I and Q signal components.
In the receiver of the mobile station, the gain changing means 105 is disposed upstream of the frequency converting means 109. The gain changing means 105 selects the attenuating means 106 or the second radio frequency amplifying means 107 corresponding to the received power so as to prevent the frequency converting means 109 that converts a radio frequency signal with a relatively high received power into an intermediate frequency signal from operating in a nonlinear region.
The variable gain means 112 causes the powers of the input signals to the A/D converting means 117 and 118 against the received power that largely varies to be kept constant.
Next, the operation of the mobile station shown in FIG. 1 will be described. When the received power of the mobile station is low, the second radio frequency amplifying means 107 of the gain changing means 105 is used. The received power calculating means 401 of the radio portion controlling means 119 calculates an average received power in each time period t with the received signal, controls the gain of the variable gain means 112, and supplies the average received power at the end of the antenna corresponding to the calculated average received power to the transmission power controlling means 403.
The transmission power controlling means 403 generates transmission power control information for the base station. The transmission signal generating means 404 places transmission power control information on transmission data and transmits the resultant signal to the base station through the transmitting means 122 and the antenna 101.
When the received power becomes relatively high, the attenuating means 106 of the gain selecting means 105 is used so as to prevent the frequency converting means 109 from operating in the non-linear region. When the gain is attenuated, the gain of the variable gain means 112 is increased for the difference between the gain of the high frequency amplifying means 107 and the gain of the attenuating means 106. The received power calculating means 401 calculates the average received power in each time period t so as to control the gain of the variable gain means 112.
However, in the receiver of the conventional mobile station, when the timing at which the gain of the gain changing means 105 is changed does not match the timing at which the gain of the variable gain means 112 is varied, the received power in the time period between the timing at which the gain of the gain changing means 105 is changed and the timing at which the gain of the variable gain means 112 is varied supplied as a low power corresponding to the gain attenuated by the attenuating means 106 of the gain changing means 105 to the received power calculating means 401. The average received power calculated in each time period t becomes lower than the real power. Thus, the transmission power controlling means 403 malfunctions. When the received power at the end of the antenna becomes large and thereby the gain of the gain changing means varies, if the timing at which the gain is changed does not match the timing at which the gain of the variable gain means is varied, the calculated value of the average received power has an error such as a phase error. Thus, the base station transmits an incorrect power control signal to the base station. Consequently, when the incorrect transmission power control signal causes the base station to increase the transmission power, the received interference powers of other subscribers increase and thereby bit error rate of other subscribers deteriorates.
In addition, when the base station decreases the transmission power due to an incorrect transmission power control signal, the local received interference power increases and thereby the local bit error rate deteriorates.
The present invention is made from the above-described point of view. An object of the present invention is to provide a mobile station that allows the average received power at the end of an antenna to be accurately calculated and thereby the transmission power of a base station to be accurately controlled even if the timing at which the gain of a gain changing means is changed does not match the timing at which the gain of a variable gain means is varied. Another object of the present invention is to provide a received power calculating method that allows an error of the average received power at which the gain is changed to decrease.
To accomplish the above-described objects, a radio portion controlling means of a receiver of a mobile station has an average time setting means. A controlling means supervises the average received power. When the average received power approaches a power at which the gain of the gain changing means should be changed, the controlling means causes a received power calculating means to increase a calculation time period for a calculation of the average received power so as to decrease the error of the average received power at which the agin of a gain changing means is changed.
An aspect of the present invention is a received power calculating method for a receiver of a mobile station for calculating an average received power and controlling a transmission power of a base station with the calculated average received power, the receiver having a gain changing means for selecting radio frequency amplifying means or attenuating means so as to prevent frequency converting means for converting a radio frequency signal into an intermediate frequency signal from operating in a saturation region, a variable gain means, disposed upstream of converting means for converting the intermediate frequency signal into a base band signal and quadrature demodulating the base band signal, for keeping the power of an quadrature demodulated signal constant, the quadrature demodulated signal being supplied to A/D converting means for converting the quadrature demodulated signal as an analog signal into a digital signal, a received power calculating means for calculating the average power of a signal received from antenna means so as to control the gain of the variable gain means, a gain changing means controlling means for controlling the gain of the changing means, a transmission power controlling means for generating a control signal that causes the base station to increase the transmission power when the power of the received channel is lower than a predetermined threshold value and for generating a control signal that causes the base station to decrease the transmission power when the power of the received channel is higher than the predetermined threshold value, and a transmission signal generating means for generating a signal that causes the transmission power controlling means to transmit the control signal to the base station, the received power calculating method, comprising the steps of supervising the average received power, and causing the received power calculating means to increase the time period for a calculation of the average received power when the average received power approaches a power at which the gain of the gain changing means should be changed so as to decrease the error of the average received power at which the gain of the gain selecting means is changed.
When the average power of the received signal of the antenna means approaches a value at which the gain of the gain changing means should be changed, the average time period in which the received power is calculated is increased so as to decrease the calculation error of the received power at which the gain of the gain changing means is changed.
The average time setting means decrease the error of the calculated result of the received power calculating means at which the gain of the gain changing means is changed so as to prevent the transmission power controlling means from malfunctioning. Thus, the received power of the mobile station can be accurately calculated. The transmission power of the base station can be accurately controlled. Thus, the bit error rate due to interference from other subscribers can be prevented from deteriorating. In addition, the interference to other subscribers can be prevented.
Referring to FIGS. 3 and 4, the gain changing means controlling means (202) has a predetermined threshold value of a received power at the antenna means of which the frequency converting means (109) operates in the saturation region. The gain changing means controlling means (202) compares the average received power received from the received power calculating means (201) with the threshold value. When the average received power exceeds the threshold value, the gain changing means controlling means (202) supplies a gain change control signal to the gain changing means (105). When the gain changing means (105) receives the gain change control signal, the gain of the gain changing means (105) is changed. When the gain changing means (105) supplies a gain change signal to the received power calculating means (201), it adds a control amount corresponding to a variation amount of the gain of the gain changing means (105) to the gain control signal of the variable gain means (112) so as to control the gain of the variable gain means (112).
Likewise, the controlling means (121) has a predetermined threshold value of a received power of the antenna means of which the frequency converting means (109) operates in the saturation region. When the controlling means (121) receives the average received power from the received power calculating means (201), the controlling means (121) compares the threshold value with the average received power. When the average received power is a value in the vicinity of the threshold value, the controlling means (121) generates a control signal that causes the average time setting means (205) to increase the time period for a calculation of the received power and supplies the control signal to the average time setting means (205). Thus, the average time setting means (205) sets a longer time period than the initial set value as the time period for the calculation of the received power to the received power calculating means (201).
When the average received power received from the received power calculating means (201) largely deviates from the threshold value, the controlling means (121) sets the initial value for the time period for the calculation of the received power to the average time setting means (205) so that the received power calculating means (201) calculates the received power with the initial set value.